Optical-based sensing devices

ABSTRACT

The present invention provides an electro-optical sensing device for detecting the presence or concentration of an analyte. More particularly, the invention relates to (but is not in all cases necessarily limited to) optical-based sensing devices which are characterized by being totally self-contained, with a smooth and rounded oblong, oval, or elliptical shape (e.g., a bean- or pharmaceutical capsule-shape) and a size which permits the device to be implanted in humans for in-situ detection of various analytes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to electro-optical sensing devices for detectingthe presence or concentration of an analyte in a liquid or gaseousmedium. More particularly, the invention relates to (but is not in allcases necessarily limited to) optical-based sensing devices which arecharacterized by being totally self-contained, with a smooth and roundedoblong, oval, or elliptical shape (e.g., a bean- or pharmaceuticalcapsule-shape) and a size which permit the device to be implanted inhumans for in-situ detection of various analytes.

2. Discussion of the Background

U.S. Pat. No. 5,517,313, the disclosure of which is incorporated hereinby reference, describes a fluorescence-based sensing device comprisingindicator molecules and a photosensitive element, e.g., a photodetector.Broadly speaking, in the context of the field of the present invention,indicator molecules are molecules one or more optical characteristics ofwhich is or are affected by the local presence of an analyte. In thedevice according to U.S. Pat. No. 5,517,313, a light source, e.g., alight-emitting diode (“LED”), is located at least partially within alayer of material containing fluorescent indicator molecules or,alternatively, at least partially within a wave guide layer such thatradiation (light) emitted by the source strikes and causes the indicatormolecules to fluoresce. A high-pass filter allows fluorescent lightemitted by the indicator molecules to reach the photosensitive element(photodetector) while filtering out scattered light from the lightsource.

The fluorescence of the indicator molecules employed in the devicedescribed in U.S. Pat. No. 5,517,313 is modulated, i.e., attenuated orenhanced, by the local presence of an analyte. For example, theorange-red fluorescence of the complextris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) perchlorate isquenched by the local presence of oxygen. Therefore, this complex can beused advantageously as the indicator molecule in an oxygen sensor.Indicator molecules whose fluorescence properties are affected byvarious other analytes are known as well.

Furthermore, indicator molecules which absorb light, with the level ofabsorption being affected by the presence or concentration of ananalyte, are also known. See, for example, U.S. Pat. No. 5,512,246, thedisclosure of which is incorporated by reference, which disclosescompositions whose spectral responses are attenuated by the localpresence of polyhydroxyl compounds such as sugars. It is believed,however, that such light-absorbing indicator molecules have not beenused before in a sensor construct like that taught in U.S. Pat. No.5,517,313 or in a sensor construct as taught herein.

In the sensor described in U.S. Pat. No. 5,517,313, the material whichcontains the indicator molecules is permeable to the analyte. Thus, theanalyte can diffuse into the material from the surrounding test medium,thereby affecting the fluorescence of the indicator molecules. The lightsource, indicator molecule-containing matrix material, high-pass filter,and photodetector are configured such that fluorescent light emitted bythe indicator molecules impacts the photodetector such that anelectrical signal is generated that is indicative of the concentrationof the analyte in the surrounding medium.

The sensing device described in U.S. Pat. No. 5,517,313 represents amarked improvement over devices which constitute prior art with respectto U.S. Pat. No. 5,517,313. There has, however, remained a need forsensors that permit the detection of various analytes in an extremelyimportant environment—the human body. Moreover, further refinements havebeen made in the field, which refinements have resulted in smaller andmore efficient devices.

U.S. Pat. Nos. 6,400,974 and 6,711,423, the disclosures of which areincorporated herein by reference, each describe a fluorescence-basedsensing device comprising indicator molecules and a photosensitiveelement that is designed for use in the human body.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an electro-optical sensingdevice. In one particular embodiment, the sensing device includes: ahousing having an outer surface; a plurality of indicator moleculeslocated on at least a portion of the outer surface of the housing; acircuit board housed within the housing; a support member having a sidethat lies on a plane that is substantially perpendicular to a plane onwhich a top side of the circuit board lies; a radiation source attachedto the side of the support member and positioned a distance above thetop side of the circuit board; and a photodetector connected to thecircuit board for detecting a response of the indicator molecules.

Advantageously, to facilitate attachment of the support member to thecircuit board, the circuit board may have a groove in the top sidethereof and the support member may have an end inserted into the groove.

The sensing device may further include a reflector that is spaced apartfrom the radiation source and that has a reflective side that faces theradiation source. The photodetector may be positioned in a locationbeneath a region between the radiation source and the reflective side ofthe reflector.

In another embodiment, the sensing device includes: a housing having anouter surface; a plurality of indicator molecules located on at least aportion of the outer surface of the housing; a circuit board housedwithin the housing; a photodetector having a top side and a bottom side,wherein the photodetector is electrically connected to a circuit on thecircuit board and at least a top side of the photodetector isphotosensitive; a filter having a top side and a bottom side, the bottomside being positioned over the top side of the photodetector; and aradiation source positioned over the top side of the filter.

In some embodiments, the sensing device may further include a basehaving a top side and a bottom side, with the bottom side being attachedto an end of the circuit board, and with the bottom side of thephotodetector being mounted on the top side of the base. Preferably, thetop side of the base lies in a plane that is substantially perpendicularto a plane on which a top side of the circuit board lies and the topside of the photodetector is generally parallel with the top side of thebase. To facilitate attachment of the base to the circuit board, thebottom side of the base may have a groove therein, and an end of thecircuit board may be inserted into the groove.

In other configurations, the top side of the photodetector lies in aplane that is substantially parallel with a plane on which a top side ofthe circuit board lies. Additionally, an opaque base may be disposedbetween the radiation source and the filter. The base may be made frommolybdenum.

The above and other features and advantages of the present invention, aswell as the structure and operation of preferred embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, help illustrate various embodiments of the presentinvention and, together with the description, further serve to explainthe principles of the invention and to enable a person skilled in thepertinent art to make and use the invention. In the drawings, likereference numbers indicate identical or functionally similar elements.Additionally, the left-most digit(s) of a reference number identifiesthe drawing in which the reference number first appears.

FIG. 1 is a schematic, section view of a fluorescence-based sensoraccording to an embodiment of the invention.

FIG. 2 is a schematic, section view of a fluorescence-based sensoraccording to another embodiment of the invention.

FIG. 3 is a perspective, top view of a circuit board according to anembodiment of the invention.

FIG. 4 is a schematic, section view of a fluorescence-based sensoraccording to another embodiment of the invention.

FIG. 5 is a schematic, section view of an assembly according to anembodiment of the invention.

FIG. 6 is a schematic, section view of a fluorescence-based sensoraccording to another embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a schematic, section view of an optical-based sensor(“sensor”) 110, according to an embodiment of the invention, thatoperates based on the fluorescence of fluorescent indicator molecules116. As shown, sensor 110 includes a sensor housing 112. Sensor housing112 may be formed from a suitable, optically transmissive polymermaterial. Preferred polymer materials include, but are not limited to,acrylic polymers such as polymethylmethacrylate (PMMA).

Sensor 110 may further include a matrix layer 114 coated on at leastpart of the exterior surface of the sensor housing 112, with fluorescentindicator molecules 116 distributed throughout the layer 114 (layer 114can cover all or part of the surface of housing 112).

Sensor 110 further includes a radiation source 118, e.g. a lightemitting diode (LED) or other radiation source, that emits radiation,including radiation over a range of wavelengths which interact with theindicator molecules 116. For example, in the case of afluorescence-based sensor, radiation sensor 118 emits radiation at awavelength which causes the indicator molecules 116 to fluoresce. Sensor110 also includes a photodetector 120 (e.g. a photodiode,phototransistor, photoresistor or other photosensitive element) which,in the case of a fluorescence-based sensor, is sensitive to fluorescentlight emitted by the indicator molecules 116 such that a signal isgenerated by the photodetector 120 in response thereto that isindicative of the level of fluorescence of the indicator molecules. Twophotodetectors 120 a and 120 b are shown in FIG. 1 to illustrate thatsensor 110 may have more than one photodetector. Source 118 may beimplemented using, for example, LED model number EU-U32SB from NichiaCorporation (www.nichia.com). Other LEDs may be used depending on thespecific indicator molecules applied to sensor 110 and the specificanalytes of interested to be detected.

The indicator molecules 116 may be coated on the surface of the sensorbody or they may be contained within matrix layer 114 (as shown in FIG.1), which comprises a biocompatible polymer matrix that is preparedaccording to methods known in the art and coated on the surface of thesensor housing 112. Suitable biocompatible matrix materials, whichpreferably are permeable to the analyte, include some methacrylates(e.g., HEMA) and hydrogels which, advantageously, can be madeselectively permeable—particularly to the analyte—i.e., they perform amolecular weight cut-off function.

Sensor 110 may be wholly self-contained. In other words, the sensor ispreferably constructed in such a way that no electrical leads extendinto or out of the sensor housing 112 to supply power to the sensor(e.g., for driving the source 118) or to transmit signals from thesensor. Rather, sensor 110 may be powered by an external power source(not shown), as is well known in the art. For example, the externalpower source may generate a magnetic field to induce a current ininductive element 142 (e.g., a copper coil or other inductive element).Additionally, circuitry 166 may use inductive element 142 to communicateinformation to an external data reader. Circuitry 166 may includediscrete circuit elements, an integrated circuit (e.g., an applicationspecific integrated circuit (ASIC), and/or other electronic components).The external power source and data reader may be the same device.

In an alterantive embodiment, the sensor 110 may be powered by aninternal, self-contained power source, such as, for example,microbatteries, micro generators and/or other power sources.

As shown in FIG. 1, many of the electro-optical components of sensor 110are secured to a circuit board 170. Circuit board 170 providescommunication paths between the various components of sensor 110.

As further illustrated in FIG. 1, optical filters 134 a and 134 b, suchas high pass or band pass filters, may cover a photosensitive side ofphotodetectors 120 a and 120 b, respectively. Filter 134 a may preventor substantially reduce the amount of radiation generated by the source118 from impinging on a photosensitive side 135 of the photodetector 120a. At the same time, filter 134 a allows fluorescent light emitted byfluorescent indicator molecules 116 to pass through to strikephotosensitive side 135 of the photodetector 120 a. This significantlyreduces “noise” in the photodetector signal that is attributable toincident radiation from the source 118.

According to one aspect of the invention, an application for which thesensor 110 was developed—although by no means the only application forwhich it is suitable—is measuring various biological analytes in thehuman body. For example, sensor 110 may be used to measure glucose,oxygen, toxins, pharmaceuticals or other drugs, hormones, and othermetabolic analytes in the human body. The specific composition of thematrix layer 114 and the indicator molecules 116 may vary depending onthe particular analyte the sensor is to be used to detect and/or wherethe sensor is to be used to detect the analyte (i.e., in the blood or insubcutaneous tissues). Preferably, however, matrix layer 114, ifpresent, should facilitate exposure of the indicator molecules to theanalyte. Also, it is preferred that the optical characteristics of theindicator molecules (e.g., the level of fluorescence of fluorescentindicator molecules) be a function of the concentration of the specificanalyte to which the indicator molecules are exposed.

To facilitate use in-situ in the human body, the housing 112 ispreferably formed in a smooth, oblong or rounded shape. Advantageously,it has the approximate size and shape of a bean or a pharmaceuticalgelatin capsule, i.e., it is on the order of approximately 500 micronsto approximately 0.85 inches in length L and on the order ofapproximately 300 microns to approximately 0.3 inches in diameter D,with generally smooth, rounded surfaces throughout. This configurationpermits the sensor 110 to be implanted into the human body, i.e.,dermally or into underlying tissues (including into organs or bloodvessels) without the sensor interfering with essential bodily functionsor causing excessive pain or discomfort.

In some embodiments, a preferred length of the housing is approx. 0.5inches to 0.85 inches and a preferred diameter is approx. 0.1 inches to0.11 inches.

In the embodiment shown in FIG. 1, source 118 is elevated with respectto a top side 171 of circuit board 170. More specifically, in theembodiment shown, source 118 is fixed to a support member 174, whichfunctions to elevate source 118 above side 171 and to electricallyconnect source 118 to circuitry on board 170 so that power can bedelivered to source 118. The distance (d) between source 118 and side171 generally ranges between 0 and 0.030 inches. Preferably, thedistance (d) ranges between 0.010 and 0.020 inches. Support member 174may be a circuit board. Circuit board 170 may have a groove 180 forreceiving a proximal end 173 of member 174. This feature is furtherillustrated in FIG. 3, which is a perspective, top view of board 170.

In some embodiments, support member 174 may include an electricalcontact 158 (e.g., a conductive pad or other device for conductingelectricity) disposed on a surface thereof and electrically connected tosource 118. The contact 158 electrically connects to a correspondingelectrical contact 157 that may be disposed in groove 180 through anelectrical interconnect 159 (e.g., a circuit trace or other transmissionline). Contact 157 may be electrically connected to circuit 166 or othercircuit on circuit board 170. Accordingly, in some embodiments, there isan electrical path from circuit 166 to source 118.

As further shown in FIG. 1, a reflector 176 may be attached to board 170at an end thereof. Preferably, reflector 176 is attached to board 170 sothat a face portion 177 of reflector 176 is generally perpendicular toside 171 and faces source 118. Preferably, face 177 reflects radiationemitted by source 118. For example, face 177 may have a reflectivecoating disposed thereon or face 177 may be constructed from areflective material.

Referring now to photodetectors 120, photodetectors 120 are preferablydisposed below a region of side 171 located between source 118 andreflector 176. For example, in some embodiments, photodetectors 120 aremounted to a bottom side 175 of board 170 at a location that is below aregion between source 118 and reflector 176. In embodiments where thephotodetectors 120 are mounted to bottom side 175 of board 170, a holefor each photodetector 120 is preferably created through board 170. Thisis illustrated in FIG. 3. As shown in FIG. 3, two holes 301 a and 301 bhave been created in board 170, thereby providing a passageway for lightfrom indicator molecules 116 to reach photodetectors 120. The holes incircuit board 170 may be created by, for example, drilling, lasermachining and the like. Preferably, each photodetector 120 is positionedsuch that light entering the hole is likely to strike a photosensitiveside of the photodetector 120, as shown in FIG. 1. This technique alsodiminishes the amount of ambient light striking photodetector 120.

As further illustrated in FIG. 1, each hole in board 170 may be containa filter 134 so that light can only reach a photodetector 120 by passingthrough the corresponding filter 134. The bottom side and all sides ofthe photodetectors 120 may be covered with black light blocking epoxy190 to further diminish the amount of ambient light strikingphotodetector 120.

In one embodiment, photodetector 120 a is used to produce a signalcorresponding to the light emitted or adsorbed by indicator molecules116 and photodetector 120 b is used to produce a reference signal. Inthis embodiment, a fluorescent element 154 may be positioned on top offilter 134 b. Preferably, fluorescent element 154 fluoresces at apredetermined wavelength. Element 154 may be made from terbium or otherfluorescent element that fluoresces at the predetermined wavelength. Inthis embodiment, filter 134 a and filter 134 b filter differentwavelengths of light. For example, filter 134 a may filter wavelengthsbelow 400 nm and filter 134 b may filter wavelengths below 500 nm.

Referring now to FIG. 2, FIG. 2 illustrates a sensor 210 according toanother embodiment of the invention. As shown in FIG. 2, sensor 210 issimilar to sensor 110. A primary difference being that reflector 176 isreplaced by a support member 202, which is connected to end 194 of board170 and to which source 118 is fixed. In this embodiment, and supportmember 174 is replaced with a reflector 209. Like reflector 176,reflector 209 has a reflective face 211 that faces source 118.Additionally, so that photodetector 120 a remains closer to source 118,photodetector 120 a may switch places with photodetector 120 b andfilter 134 a may switch places with filter 134 b. Fluorescent element154 may also be re-positioned so that it remains on top of filter 134 b.

As shown in FIGS. 1 and 2, in some embodiments, indicator molecules 116may be positioned only in a region that is above a region 193, whichregion is between source 118 and reflector 176.

Referring now to FIG. 4, FIG. 4 is a schematic, section view of anoptical-based sensor 410, according to another embodiment of theinvention. Sensor 410 includes many of the same components as sensor110. However, the positioning of source 118, photodetector 120 a andfilter 134 a in sensor 410 is different than the positioning in sensor110.

As shown in FIG. 4, a base 412 is mounted to an end 413 of circuit board170. A top side 414 and bottom side 416 of base 412 each may lie in aplane that is generally perpendicular to a plane in which side 171 ofboard 170 lies. Bottom side 416 may have a groove 418 therein thatreceives end 413 of board 170. Groove 418 facilitates fixing base 412 toboard 170.

Photodetector 120 a may be mounted on top side 414 of base 412.Preferably, photodetector 120 a is mounted on base 412 so thatphotosensitive side 135 of photodetector 120 a lies in a plane that isgenerally perpendicular to the plane in which side 171 of board 170 liesand faces in the same direction as top side 414.

Filter 134 a is preferably disposed above side 135 of photodetector 120a so that most, if not all, light that strikes side 135 must first passthrough filter 134 a. Filter 134 a may be fixedly mounted tophotodetector 120 a. For example, a refractive index (RI) matching epoxy501 (see FIG. 5) may be used to fix filter 134 a to photodetector 120 a.

In some embodiments, base 412 may include at least two electricalcontacts disposed thereon (e.g., on side 414). For example, as shown inFIG. 4, a first electrical contact 471 and a second electrical contact472 are disposed on side 414 of base 412. A wire 473 (or otherelectrical connector) preferably electrically connects photodetector 120a to electrical contact 471 and a wire 474 (or other electricalconnector) preferably electrically connects source 118 to electricalcontact 472. Contact 471 electrically connects to a correspondingcontact 475 via an electrical interconnect 476. Similarly, contact 472electrically connects to a corresponding contact 477 via an electricalinterconnect 478. Contacts 475, 477 are preferably disposed on the endof board 170 that is inserted into groove 418. Contacts 475, 477 may beelectrically connected to circuit 166 or other circuit on circuit board170. Accordingly, in some embodiments, base 412 provides a portion of anelectrical path from circuit 166 to source 118 and/or photodetector 120a.

Referring now to FIG. 5, FIG. 5 further illustrates the arrangement ofphotodetector 120 a, filter 134 a and source 118. As shown in FIGS. 4and 5, source 118 is mounted on a top side 467 of filter 134 a.Accordingly, as shown in FIG. 4 and 5, photodetector 120 a, filter 134 aand source 118 are aligned. That is, as shown in FIG. 5, both filter 134a and source 118 are each disposed in an area that is over at least aportion of photosensitive side 135 of photodetector 120 a.

Preferably, a non-transparent, non-translucent base 431 is disposedbetween source 118 and filter 134. Opaque base 431 functions to preventlight emitted from source 118 from striking side 467 of filter 134 a.Base 431 may be a gold-clad-molybdenum tab (molytab) or other opaquestructure. Epoxy 555 may be used to fix source 118 to base 431 and base431 to filter 134 a.

Preferably, in this embodiment, source 118 is configured and oriented sothat most of the light transmitted therefrom is transmitted in adirection away from side 467, as shown in FIGS. 4 and 5. For example, inthe embodiment shown, the light is primarily directed towards an end 491of housing 102. Preferably, indicator molecules 116 are located on end491 so that they will receive the radiation emitted from source 118. Asdiscussed above, indicator molecules 116 will respond to the receivedradiation, and the response will be a function of the concentration ofthe analyte being measured in the region of the indicator molecules 116.Photodetector 120 a detects the response.

Referring now to FIG. 6, FIG. 6 is a schematic, section view of anoptical-based sensor 610, according to another embodiment of theinvention. Sensor 610 includes many of the same components as sensor110. Also, sensor 610 is similar to sensor 410 in that, in sensor 610,photodetector 120 a, filter 134 a and source 118 are preferably aligned.Further, like in sensor 410, in sensor 610 filter 134 a may be fixedlymounted on side 135 of photodetector 120 a and source 118 may be fixedlymounted on side 467 of filter 134 a, and the photodetector 120 a, filter134 a, source 118 assembly may be located adjacent an end 491 of housing102, as illustrated in FIG. 6.

However, the orientation of source 118, photodetector 120 a and filter134 a in sensor 610 is different than the orientation in sensor 410. Forexample, in sensor 610, side 135 of photodetector 120 a faces in adirection that is substantially perpendicular to the longitudinal axisof housing 102. Additionally, in sensor 610, filter 134 a and/orphotodetector 120 a are directly fixed to board 170 such that base 412may be removed. In the embodiment shown, filter 134 a and/orphotodetector 120 a are directly fixed to end 413 of board 170.

In one or more of the above described embodiments, housing 102 may befilled with a material to keep the components housed in housing 102 frombeing able to move around. For example, housing 102 may be filled withan optical epoxy either before or after board 170 and the componentsattached thereto are inserted into housing 120. EPO-TEK 301-2 Epoxy fromEpoxy Technology of Billerica, Mass. and/or other epoxies may be used.

While various embodiments/variations of the present invention have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. Thus, the breadth and scopeof the present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

1. An electro-optical sensing device for detecting the presence orconcentration of an analyte, comprising: a housing having an outersurface; a plurality of indicator molecules located on at least aportion of the outer surface of the housing; a circuit board housedwithin the housing; a support member having a side that lies on a planethat is substantially perpendicular to a plane on which a top side ofthe circuit board lies; a radiation source attached to said side of thesupport member and positioned a distance above the top side of thecircuit board; and a photodetector attached to the circuit board fordetecting a response of the indicator molecules.
 2. The sensing deviceof claim 1, wherein said circuit board has a groove in the top sidethereof and said support member has an end inserted into said groove. 3.The sensing device of claim 1, wherein the distance ranges between about0.010 inches and 0.030 inches.
 4. The sensing device of claim 1, furthercomprising a reflector spaced apart from the radiation source and havinga reflective side that faces the radiation source.
 5. The sensing deviceof claim 4, wherein the photodetector is positioned in a locationbeneath a region between the radiation source and the reflective side ofthe reflector.
 6. The sensing device of claim 5, wherein thephotodetector has a photosensitive side that faces in a directionsubstantially perpendicular to the direction that the reflective side ofthe reflector faces.
 7. The sensing device of claim 6, wherein thephotosensitive side of the photodetector is positioned below the topside of the circuit board.
 8. The sensing device of claim 7, wherein thecircuit board has a hole that extends from the top side to a bottomside.
 9. The sensing device of claim 8, wherein the photodetector isattached to the bottom side of the circuit board.
 10. The sensing deviceof claim 4, wherein said circuit board has a groove in the top sidethereof and said reflector has an end inserted into said groove.
 11. Thesensing device of claim 1, wherein a first electrical contact isdisposed on a surface of the support member and the radiation source iselectrically connected to the electrical contact.
 12. The sensing deviceof claim 11, wherein the first electrical contact is electricallyconnected to a second electrical contact disposed on the circuit board.13. The sensing device of claim 12, further comprising a circuit tracedisposed on or within the support member that functions to electricallyconnect the first electrical contact with the second electrical contact.14. An electro-optical sensing device for detecting the presence orconcentration of an analyte, comprising: a housing having an outersurface; a plurality of indicator molecules located on at least aportion of the outer surface of the housing; a circuit board housedwithin the housing; a photodetector having a top side and a bottom side,wherein the photodetector is electrically connected to a circuit on thecircuit board and at least a top side of the photodetector isphotosensitive; a filter having a top side and a bottom side, the bottomside being positioned over the top side of the photodetector; and aradiation source positioned over the top side of the filter.
 15. Thesensor of claim 14, further comprising a base having a top side and abottom side, the bottom side being attached to an end of the circuitboard, wherein the bottom side of the photodetector is mounted on thetop side of the base.
 16. The sensor of claim 15, wherein the top sideof the base lies in a plane that is substantially perpendicular to aplane on which a top side of the circuit board lies.
 17. The sensor ofclaim 16, wherein the top side of the photodetector is generallyparallel with the top side of the base.
 18. The sensor of claim 15,wherein the bottom side of the base has a groove therein, and the end ofthe circuit board is inserted into the groove.
 19. The sensor of claim15, further comprising: a first electrical contact disposed on the base;and a second electrical contact disposed on the base, wherein thephotodetector is electrically connected to the first electrical contact,and the radiation source is electrically connected to the secondelectrical contact.
 20. The sensor of claim 19, wherein the firstelectrical contact is electrically connected to a third electricalcontact disposed on the circuit board and the second electrical contactis electrically connected to a fourth electrical contact disposed on thecircuit board.
 21. The sensor of claim 20, further comprising a circuittrace disposed on or within the base that functions to electricallyconnect the first electrical contact with the third electrical contactand the second electrical contact with the fourth electrical contact.22. The sensor of claim 14, wherein the top side of the photodetectorlies in a plane that is substantially parallel with a plane on which atop side of the circuit board lies.
 23. The sensor of claim 14, furthercomprising an opaque base disposed between the radiation source and thefilter.
 24. The sensor of claim 23, wherein the base comprisesmolybdenum.
 25. The sensor of claim 14, wherein the filter is fixed tothe photodetector using an epoxy.
 26. The sensor of claim 25, whereinthe epoxy is disposed between the bottom side of the filter and the topside of the photodetector.
 27. The sensor of claim 26, wherein thereflective index of the epoxy matches the reflective index of thefilter.
 28. The sensor of claim 14, wherein the radiation source islight emitting diode.